<!DOCTYPE html>
<html lang="en">
<head>
  <meta charset="UTF-8">
  <meta http-equiv="X-UA-Compatible" content="IE=edge">
  <meta name="viewport" content="width=device-width, initial-scale=1.0">
  <title>Document</title>
  <style>
    body {
      margin: 0;
      padding: 0;
    }
    div{
      width: 300px;
      height: 300px;
      margin: 100px 250px;
      background: pink;
    }
  </style>
</head>
<body>
  <div></div>

  <script>
    var div = document.querySelector('div')

    div.onmousemove = function(e) {
      var x = e.pageX - this.offsetLeft
      var y = e.pageY - this.offsetTop

      this.innerHTML = 'x:' + x + ', y:' + y

    }
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</body>
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